In an IEEE 802.11 compliant communications system (also known as WiFi), an access point (AP) serves one or more stations (STA) by receiving transmissions from the one or more STA and forwarding the transmissions to their intended destinations. Similarly, the AP receives a transmission intended for one of its STA and forwards the transmission to the STA. A transmission occurs over unidirectional channels referred to as communications links. A transmission from a STA to the AP may be referred as an uplink (UL) transmission, while a transmission from the AP to a STA may be referred to as a downlink (DL) transmission.
FIG. 1 illustrates a portion of a prior art beacon 100. Beacon 100 is transmitted periodically by an AP and includes an element identifier (element ID) field 105, a length field 110, a delivery traffic indication map (DTIM) count field 115, a DTIM period field 120, a bitmap control field 125, and a partial virtual bitmap field 130. Element ID field 105, length field 110, DTIM count field 115, DTIM period field 120, and bitmap control field 125 contain information identifying and specifying a traffic indication map (TIM) bitmap contained in partial virtual bitmap field 130. The TIM bitmap is maintained by the AP or a mesh STA and consists of up to 2008 bits organized into 251 octets. An N-th bit (0≦N≦2007) in the TIM bitmap corresponds to bit number (N mod 8) in octet └N/8┘ where a low-order bit of each octet is bit number 0 and a high-order bit of each octet is bit number 7. Each bit in the TIM bitmap corresponds to traffic (data) buffered for a specific STA in a basic service set (BSS) that the AP is going to transmit at a time that beacon 100 is transmitted or a specific neighbor peer mesh STA within the mesh BSS (MBSS) that the mesh STA is going to transmit at a time that beacon 100 is transmitted.
The N-th bit in the TIM bitmap is set to “0” if there is no data (e.g., individually addressed MAC service data unit (MSDU) and/or MAC management protocol data unit (MMPDU)) for the STA corresponding to the N-th bit. If there are any individually addressed data, e.g., MSDU and/or MMPDU, for the STA corresponding to the N-th bit, then the N-th bit in the TIM bitmap is set to “1”. It is noted that in legacy IEEE 802.11 systems, e.g., those that are compliant to IEEE 802.11 a, 802.11 g, 802.11 n, 802.11 ac, and the like, the maximum number of STAs in a BSS is 2007, so the TIM bitmap is capable of representing all STAs of a single BSS.